The present invention relates to a control system for controlling the movement of conveyor carriages along a conveyor rail.
Conveyor systems in which several travelling units or carriages travel along a conveyor rail have found widespread acceptance in virtually every form of manufacturing operations. Such systems have proven invaluable in transporting individual parts and sub-assemblies between storage areas and work stations. Conveyor systems with individually powered carriages moving along the conveyor have proven most satisfactory insofar as they allow each carriage to move separately thereby enabling stops of varying durations at each work station.
However, the use of such conveyors having individually powered carriages has also required some means to prevent the moving carriage from colliding with a carriage which has stopped. Sophisticated sensing systems have been provided to sense the presence of a stopped carriage, or other obstacle present in the path of a moving carriage. These systems typically require each carriage to have sensors positioned both in the front and the back to prevent the carriages from colliding.
While these systems have proven generally satisfactory, they often fail to prevent carriage collisions where the conveyor rail is curved and wherein a stopped or slowly moving carriage is located on one side of the curve and the more rapidly moving carriage is located on the other side of the curve. In this situation, the stopped or slowly moving carriage is usually outside of the range of the sensors of the faster moving carriage. Thus, the sensors on the faster moving carriage are unable to detect the presence of the stopped or slower moving carriage and collisions often result.
Also, the requirement to place such sophisticated sensors on each carriage increases the cost and complexity of the conveyor system. Such increase in complexity inherently reduces the reliability of such a conveyor system, especially when located in an industrial environment.